Musannaf Ibn Abi Shayba 3:2153

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Nu’aym ibn Hakim narrated to us, from Abu Maryam al-Thaqafi, who said: Al-Hasan ibn Ali led us in the Maghrib prayer. When he finished the prayer, he performed two prostrations, and we did not see him make a mistake. When he performed the taslim, we asked him [about it], and he said: "I made a mistake."